Natural antidepressant has its limitations.

For over 2,000 years, people have been taking St. John's wort to escape bouts of anxiety and depression. But this plant with small yellow flowers isn't for everybody, according to a new study.

St. John's wort, now popular as an ingredient in herbal remedies, doesn't help people with moderate or severe forms of depression, concludes the team of psychiatrists that conducted the study. Since the risks of inadequate treatment for major depression are so high, the scientists conclude that people with serious depression "should not be treated with St. John's wort."

Many people with depression have preferred St. John's wort over conventional drugs because of its lower cost and fewer side effects, says study leader Richard C. Shelton of Vanderbilt University in Nashville. Many studies on St. John's wort have bolstered anecdotal evidence that the natural antidepressant is more effective at relieving depression than a placebo is (SN: 10/30/99, p. 280). Several experiments even found that St. John's wort worked as well as some standard antidepressant drugs. However, Shelton says there are flaws in that research.

The previous work, for example, didn't distinguish patients with milder forms of depression from those with more severe depression, he says. So, he and his colleagues focused their research on moderately to severely depressed people--the population that would be harmed most if treatment failed. Discouraged by unrelenting symptoms, these people can become suicidal, says Shelton.

The researchers recruited 200 adults diagnosed with moderate to severe depression. All the patients had been depressed for at least 4 weeks before the study and had not taken St. John's wort.

Half the patients were treated with three 300-milligram tablets of St. John's wort extract per day. If a patient didn't show improvement after the fourth week of treatment, the researchers increased the dose to four tablets a day. The other half of the patients received a similar treatment regimen, but with a placebo in place of the herb.

After 8 weeks, the researchers found no significant difference in depression between the two groups. Shelton and his colleagues report their findings in the April 18 JOURNAL OF THE AMERICAN MEDICAL ASSOCIATION.

James E. Simon, a medicinal plant biologist at Rutgers University in New Brunswick, N.J., notes that the new work confirms a "long-held belief" that people who have moderate or severe depression shouldn't rely on St. John's wort.

"There's a window of opportunity where [St. John's wort] looks like it's effective," and that's only for people with mild depression, says Simon.

Shelton notes that his team's findings have no bearing on the herb's effectiveness in people with mild depression and says that on that matter, "the jury's still out."